The present invention relates to the deposition of useful material layers on substrates, including semiconductor substrates. More particularly, the present invention relates to the field of depositing useful layers on substrates and filling holes in the uppermost material layers previously formed on the substrate to create interconnects, plugs, or other structures within the multiple material layers ultimately formed on the substrate.
The formation of microelectronic circuitry on semiconductor substrates depends, in part, on the preparation of interconnects, plugs, or other such devices through, or between, the various layers formed on the substrate surface. These structures are typically created by depositing a film of conductive material over the uppermost dielectric material layer or layers on the substrate, such that a portion of the conductive deposition layer fills any holes in the dielectric material layer or layers previously formed on the substrate. One typical method of providing this conductive material layer is by sputtering a target to supply particles of target material that may deposit on the substrate.
Where sputtering is used to form a material layer on the base and walls of a hole, the thickness of the layer formed on the walls of the hole, known as the step coverage, is typically only a percentage of the thickness of the material layer that forms on the upper surface of the substrate. This occurs because the geometric configuration of a hole prevents a portion of the target material particles travelling in the direction of the wall of the hole from reaching the wall of the hole, whereas the generally flat upper surface of the substrate has no such limiting geometric configuration. Where the aspect ratio of the hole is high, i.e., the hole depth is large with respect to the hole width, the percentage of available target material particles that deposit on the wall of the hole varies with the depth of the hole. Typically, the step coverage is thicker at the upper regions of the hole as compared to the step coverage at the lower regions of the hole. Therefore, where the hole has a high aspect ratio, the base of the hole may have inadequate step coverage, or areas of no coverage, ultimately creating a defect in the device at that location on the substrate.